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Tryon's Rat Experiment

Robert Tryon Background

Robert Choate Tryon was born in Butte, Montana on September 4th in the year 1901. Tryon spent most of his life at the University of California Berkeley campus. He received his AB degree from the undergraduate school in 1924, and as a graduate student he earned his Ph.D in 1928. After graduating from the school he spent two years as a National Research Council fellow. In 1931, he became a faculty member of the college’s Department of Psychology, which he was a member of for 31 years. During the war he served in Washington DC as the deputy chief of the planning staff for the Office of Strategic Services. Aside from that short period, he was always in Berkeley. On September 27, 1967 he died in Berkeley, California.

Experiment Set-Up

Tyron's rat chart

Previous to Robert Tryon’s study of selective breeding, concluded in 1942, many psychologists believed that environmental, rather than genetic, differences produced individual behavioral variations. Tryon sought to demonstrate that genetic traits often did, in fact, contribute to behavior. To do so, Tryon created an experiment that tested the proficiency of successive generations of rats in completing a maze. He initiated the experiment by exposing a genetically diverse group of rats to the maze, labeling those who made the fewest errors “bright,” and those with the most errors “dull.” Tryon then mated the “bright” males with “bright” females, and “dull” males with “dull” females. After their children matured, Tryon repeated the maze test with them, and again separated the “bright” and the “dull,” again breeding “bright” with “bright” and “dull” with “dull.” Tryon continued this process for seven generations, creating two distinct breeds of “bright” and “dull” rats. In order to demonstrate that behavior had little effect on the genetically selectively bred rats, and lessen the chance of error when making his conclusions, Tryon cross-fostered the rats—that is, he had a “dull” mother raise “bright” children, and vise-versa. The independent variables in his experiment were the parental pairings, the choice of environment and parents for upbringing, and number of rats put through the maze. The dependent variable was the number of errors made by the rats in 19 trials of the maze.

Implications and Conclusions

While Tryon's results showedd that the “bright rats” made significantly fewer errors in the maze than the “dull rats” did, the question of what other sensory, motor, motivational, and learning processes also influenced the results of the experiment exists. A common misconception of this experiment and other similar experiments is that the observed change in the performance in the maze directly correlates with general learning ability, but this is not the case. Rather, it has become a widely accepted believe among behavior geneticists that the superiority of the bright rats was confined to Tryon’s specific test; thus, it is not possible to claim that there is a difference in learning capacity between the two groups of rats. Genetic variation, such as better peripheral vision, can make some rats “bright” and others “dull,” but does not determine their intelligence. Nonetheless, Tryon’s famous rat-maze experiment demonstrated that the difference between rat performances was genetic since their environments were controlled and identical.

See also

• Selective breeding
• Gene-environment interaction
• Genetic variation
• Artificial selection
• Nature vs. nurture
• UC Berkeley